This invention relates in general to a sensing device with an improved signal to noise ratio for use in an electrically noisy environment. Specifically this invention relates to a synchronized discriminator sensing device for sheet media within an automated transaction machine, including an automated teller machine or any other machine capable of carrying out transfers representative of value.
Automated transaction machines, and particularly automated teller machines (ATMs) used to carry out banking transactions, are operated using electrical circuitry and components including motors, transformers, relays, solenoids and other actuating devices, all of which generate unwarranted electrical signals or xe2x80x9cnoisexe2x80x9d.
One important ATM function is dispensing and receiving sheets. Such sheets may be of several types. A common type of sheet dispensed is currency in the form of currency notes or bills. On occasion two or more bills may adhere to each other due to the surface condition of the bills or humidity or other weather conditions. It is desirable for this condition to be detected before the bills are dispensed. A similar condition may occur in currency receiving machines. Two or more bills adhering together introduces errors into the currency receiving process.
Mechanical thickness detection methods have been developed, but variations in surface characteristics of bills which have been in circulation as compared to new bills make thickness detection for double bills difficult. If detection in a dispensing function is not sensitive enough, multiple bills may be dispensed and a loss incurred by the ATM operator. If detection is too sensitive, thicker single bills will be diverted and not dispensed, causing the ATM to require restocking more frequently than otherwise necessary.
Electrical and optical detection methods are affected by the electrical noise in the ATM environment. Such noise affects the sensitivity at which electrical and optical methods can operate. Signal strength must be high enough that it can be detected above the electrical noise floor in the ATM. Increasing signal strength requires higher power operation. Components with higher ratings are required to operate at higher power without deteriorating sensitivity and to avoid operational problems such as signal saturation.
Radiation type sheet thickness detection devices may have their accuracy adversely affected by differences in sheet coloration. For example, a dark color sheet usually absorbs more radiation than lighter color sheets. Different materials used in currencies of different countries have different radiation absorption properties. This can make it difficult to distinguish between single and multiple sheets. This presents challenges for automated transaction machines which must distinguish between single and multiple sheets having varied radiation absorption and reflectance properties.
Thus there exists a need for an improved sheet thickness detecting device and method for distinguishing between single and multiple sheets dispensed by an automated transaction machine.
It is an object of the present invention to provide an apparatus and method for use in an automatic transaction machine, for detecting with a sensing device the thickness of sheet media being dispensed or received.
It is a further object of the present invention to provide an apparatus and method for use in an automatic transaction machine, for detecting with a sensing device the thickness of sheet media being dispensed or received, the sensing device including an optical source and an optical detector.
It is a further object of the present invention to provide an apparatus and method for use in an automatic transaction machine, for detecting with a sensing device the thickness of sheet media being dispensed or received, the sensing device including an infrared radiation source and an infrared radiation detector.
It is a further object of the present invention to provide an apparatus and method for use in an automatic transaction machine, for detecting with a sensing device the thickness of sheet media being dispensed, the sensing device including a pulsed optical source and an optical detector.
It is a further object of the present invention to provide an apparatus and method for use in an automatic transaction machine for detecting with a sensing device the thickness of sheet media being dispensed or received, the sensing device including a pulsed optical source and an optical detector synchronized with the optical source.
It is a further object of the present invention to provide an apparatus and method for use in an automatic transaction machine, for detecting with a sensing device the thickness of sheet media being dispensed or received, the sensing device including a pulsed optical source and an optical detector synchronized with the optical source and a discriminator which favors signals synchronized with the source and attenuates other signals.
It is a further object of the present invention to provide an apparatus and method for use in an automatic transaction machine, for detecting with a sensing device the thickness of sheet media being dispensed or received, the sensing device including a pulsed radiation source, a synchronized radiation detector and a discriminator which is both frequency and phase sensitive.
It is a further object of the present invention to provide an apparatus and method for an automatic transaction machine, for detecting with a sensing device the thickness in sheet media being dispensed or received, the sensing device including a pulsed radiation source, a synchronized radiation detector for detecting both a reflected radiation beam and a transmitted radiation beam, and a discriminator which is both frequency and phase sensitive.
It is a further object of the present invention to provide an apparatus and method for use in an automated transaction machine which is operative to reliably distinguish between single and double sheets of sheet media having varied radiation reflectance and absorption properties.
It is a further object of the present invention to provide an apparatus and method for use in an automated transaction machine that is operative to determine the thickness of sheet media that is economical and reliable.
It is a further object of the present invention to provide a method for improving the sensing accuracy of sensing devices used in an automated banking machine.
Further objects of the present invention will be made apparent following the Best Modes for Carrying Out Invention and the appended claims.
The foregoing objects of the present invention are accomplished in an automated transaction machine one preferred embodiment. This exemplary embodiment includes a sheet thickness detector with a synchronized discriminator. The synchronized discriminator in accordance with the exemplary embodiment of the present invention comprises a radiation source, one or more radiation detectors, a preamplifier, a synchronized chopper and an integrator.
The radiation source preferably includes a light emitting diode (LED) pulsed by a driving circuit in a selected sequence. Preferably the LED includes an infrared emitter (IR LED). The IR LED illuminates a first face of a sheet, such as a currency bill, whereupon a portion of the infrared signal is reflected and a portion is transmitted through the sheet. The strength of the reflected beam is proportional to the thickness of the sheet while the strength of the transmitted beam is inversely proportional to the thickness of the sheet. That is, as the number of sheets comprising the sensed sheet media increases, more of the beam will be reflected from the media and less will be transmitted through the media. Further, both the strength of the reflected beam and the strength of the transmitted beam are generally inversely proportional to the darkness (color pattern) of the sensed sheet.
Radiation detectors for the reflective and the transmissive components are preferably photo diodes or photo transistors. In an exemplary embodiment the output of each detector is amplified and delivered to the input of a synchronized chopper circuit which is also referred to herein as a chopper. The chopper is generally synchronized to the pulse pattern driving the LED to process generally only signals synchronized with the LED. The output of the synchronized chopper is processed by an integrator circuit to generate a signal representative of the thickness of the sensed sheet(s).
Alternative embodiments of the invention may include multiple radiation sources positioned on opposed sides of the sheet media. Such embodiments may also include detectors for sensing the level of transmitted and reflected radiation from each radiation source. Each radiation source is preferably driven in a synchronized manner at different times, and the signals processed from the detectors in coordinated relation with the operating period of the radiation source of interest. Signals corresponding to the level of transmitted and reflected radiation from the radiation sources on each side of the sheet media may be combined or otherwise processed to distinguish between single and multiple sheets having varied transmission and reflectance properties. Alternative embodiments where the radiation sources can be separately detected without interference may be operated during overlapping intervals. The principles of the invention may also be used in connection with other types of sensors.